This invention relates generally to elastomer sealing rings of relatively large diameter. More particularly, this invention relates to an elastomer sealing ring which fits into an annular channel of relatively large diameter which is open to one side with a base surface and two mutually opposing side surfaces. The sealing ring has approximately the same cross-section as the channel and exhibits an exposed sealing surface, which, when the sealing ring is fitted in its channel, faces the open side of the channel and can be subjected by a sealing bead to a surface load approximately parallel to the axis of the seating.
Sealing rings of the type described above are used, for example, in larger, gastight valves. Such valves have a diameter of 0.5 to 2 meters or more. These valves are used, for example, on blast furnaces, and are exposed to substantial contact pressures. Applicant has discovered that these elastomer sealing rings of relatively large diameter can experience relatively large tears in the surface after just a relatively few load cycles. These tears, which are a priori inexplicable, are localized on the one hand in the ring surfaces facing the channel. More particularly, these tears are localized in the zones between the base surface and side surfaces and on the other hand in the exposed sealing surface.
It will be appreciated that there is a need to improve the geometry of the sealing ring in order to prevent these tears or greatly reduce these inexplicable tears discussed above.
Complex calculations of the sealing ring according to the "finite elements" method have shown, in fact, that high stresses arise at the aforementioned zones and produce tearing, primarily whenever the sealing ring is constricted in the channel. These high stresses can be observed even for a relatively low surface load applied to the exposed sealing surface.
It is generally known that an elastomer material is not compressible and therefore needs space to expand. However, according to the prior art, this factor was only taken into account insofar as the sealing ring was dimensioned such that it could be fitted with radial play into the channel. The sealing ring was therefore able to expand laterally, i.e., to yield at right-angles to the direction of load into the channel. Applicant has found, however, that this measure is not, however, sufficient to prevent the aforementioned tearing, for at least the following reasons:
a) the lateral expansion of the sealing ring inevitably produces an unfavorable stress distribution, since, for example, significant shearing forces arise between the base surface of the channel and the sealing ring;
b) it has been shown in practice that dimensional errors in sealing rings over 1 meter in diameter are generally greater than the calculated play between the sealing ring and the channel. It therefore very often happens, particularly in sealing rings of relatively large diameter, that the sealing ring fails to assume that position in the channel which allows it stress-relieving expansion; and
c) it cannot be ruled out that the radial play between the channel and the sealing ring will be lost by virtue of the seat becoming deformed or by virtue of solids getting into the channel during fitting.